Exhaust silencer for aircraft motors and the like



EXHAUST SILENCER FOR AIRCRAFT MOTORS AND THE LIKE Filed June 8, 1928 0/250/ e by Patented Oct. 14, 1930 PATENT. OFFICE OLE SOLIBERG 31E, OFOSLO, NORWAY EXHAUST SILENCE FOB AIRCRAFT MOTORS AND THE LIKEApplication filed June 8,1928, Serial No. 283951, and in France November22, 1927.

r The present invention has for its obj ect an exhaust silencer foraircraft motors and similar motors for transport means adapted to movethrough the air with high velocity, and 5 the object of the invention isto provide an exhaust silencer adapted to utilize the suction andcooling efiect of the air current in.

tively, in which zones the outlet openings for the exhaust gases fromthe silencer are located.

By giving the shell of the silencer this shape, an extremely efiicienteffect is obtained, and this eflect increases with increasing velocity,whereby the loss of motor output caused by the silencer is reduced to anunimportant value. p

The eflect of the zone with reduced air pressure and turbulent aircreated by the above mentioned shape of the shell also has a verypronounced efi'ect on the silencer action owing to the fact that thepoint or points at which the sound waves are created, that is,

the zone immediately surrounding the outlet openings, is located in amedium which is a bad conductor of sound, and this efiect also increaseswith increasing velocity and decreasing air pressure in the said zone.

At the same time the interior construction of the silencer is sodesigned that the exhaust gases before arriving at the outlet openingsfrom the silencer are caused to pass in a comparatively thin film alonga substantial part of the exterior shell of the silencer so as to besubjected to an effective cooling by means of the air through which thesilencer passes with great velocity.

If so desired, this cooling efiect may beincreased in a manner known perse by means of an air duct passing coaxially through the silencer.

The accompanying drawing illustrates two modifications of the invention,in which similar reference numerals refer to similar parts and wherein:

I Figure 1 is a longitudinal axial cross-section of the exhaustsilencer.

Figure 2 is a longitudinal axial cross-section of a modification of theexhaust silencer.

Referring, now, to Figure 1, the exhaust gases are conducted through theexhaust tubes 1 into a collecting chamber 2, the introduction into thischamber taking place in a tangential direction, so that the gas currentsare caused to pass through the collecting chamber along helical lines. A

From the collecting chamber 2 the exhaust gas is conducted through aVenturi tube 3 with reduced cross section into a distributing chamber 4.

The Venturi tube 3 is shaped in accordance with the Venturi-principle inorder to produce a suction effect between the collecting" chamber 2 andthe distributing chamber 4.

The distributing chamber 4 preferably taperstowards the rear and isprovided with outlet openings 4' distributed over the walls thereof inthe longitudinal direction.

' Through the said outlet openings 4 the exhaust gas passes'into asilencer chamber 5 between the exterior walls of the distribu tingchamber 4 and a baflie 6 forcing the sev eral gas currents from theoutlet openings 4' in the wall of the distributing chamber 4 to passtowards the front end of the silencer. The double conical exteriorsurface of the g5 silencer chamber 5 has the effect of providing arestricted annular passage which causes another Venturi-effect to takeplace. At its front end the baflle 6 is provided with an inwardlyprojecting beaded annular rib 11, so w as to produce a smooth path forthe gas currents at the turn. a

From the annular chamber at the end of the baflle wall and to the frontend of the silencer, the exhaust gas passes through a narrow'channel 7of annular cross section, the'exterior wall of which is formed by theexterior shell 8 of the silencer, which is eifectively cooled by meansof the air through which the silencer is passing. Finally the 9 at ornear the rear end of the shell of the silencer.

Towards the rear end thereof the silencer is given a form which deviatesin such. a manner from the stream linev form that there is formed at thepart of the shell surface where the outlet openings for the exhaustgases are located, zones with reduced air pressure. This will have theeffect of producing very effective suction at the outlet openings, asuction radically different from the suction which may be obtained-owingto ejector action by letting the gases out through openings along theedges of which air currents pass With great velocity.

The difference from suction produced by ejector action is perhaps stillmore pronounced as regards the silencer action owing to the fact thatwhereas the sound in case of ejector outletsis developed at points wherethe sound waves are directly transmitted to the surrounding air, thesound waves in the present'instance are developed in a zone with aconsiderably reduced air pressure, which has the effect of damping thesound waves considerably before theyreach'air of normal pressure. v t Onthe drawing the normal stream line form for the relative velocities inquestion is indicated by means of dotted lines at the rear end of thesilencer, and it will be noted that the exterior contour of the silencerfrom a point near the largest cross section thereof is curvedconsiderably more inwards than would be the case for the normal streamline increasing the cooling action.

As many different modifications of my invention may bemade, the abovedisclosure is to be construed in an illustrative and not in a limitingsense.

Having now fully described my invention what I desire to toprotect byLetters Patent -is defined in the following claims:

1. In an exhaust silencer for aircraft motors and the like, incombination,'a plurality of exhaust conduits from the motor, acollecting chamber communicating the'rewithand having a stream lineform, an exterior shell having the front portion thereof in stream linerelation to said collecting chamberand the rear portion thereofdeviating in axial direction from said stream line form to create a zoneof turbulent air under reduced pressure at the rear of said shell,outlet open- 1ngs for the exhaust gases located in said zone and meansfor causing the exhaust gases to pass in a shallow current along asubstantial part of the interior of said exterior shell before arrivingat said outlet openings.

2. An exhaust silencer for aircraft motors and the like, having aplurality of exhaust conduits connected to the motor, a collectingchamber adapted to be connected to said exhaust conduits, a distributingchamber, a Venturi tube connecting said collecting chamber and saiddistributing chamber, an exterior shell surrounding said distributingchamber', outlet openings in the wall of said distributing chamber andmeans for-conducting the gas currents first toward the front end of saidshell and then along the inside thereof to outlet openings locatedadjacent the rear end of said shell. 1

3. An exhaust silencer for aircraft motors and the like, having acollecting chamber adapted to be connected to the exhaust conduit fromthe motor, a distributing chamber, a Venturi tube connecting saidcollecting chamber and said distributing chamber, an exterior shellsurrounding said distributing chamber, said shell having a form adaptedto create zones on its exterior surface with reduced air pressure,outlet openings in the wall of said distributing chamber and means forconducting the gas currents first towards the front end of said shelland then along the inside thereof to outlet openings located in saidzones of reduced air pressure. I

4. An exhaust silencer for aircraft motors and the like, comprising acollecting chamber adapted to be connected to the exhaust conduit fromthe motor, a distributing chamber, a Ventu'ri tube connecting saidcollecting chamber and said distributing chamber, an exterior shellsurrounding said distributing chamber, said shell having a form adaptedto create zones on its exterior surface with reduced air pressure,outlet openings distributed along the wall of said distributing chamber,a baflie between said distributing chamber and the shell, said baflieterminating adjacent the front end of said shell so as to conduct-thegas currents first towards the front end of said shell and then alongthe inside thereof to outlet openings located adjacent the rear end ofsaid shell.

'5. An-exhaust silencer for aircraft motors and the like, comprising acollecting chamber tapering towards its front end and adapted to beconnected to the exhaust conduit from the motor, a distributing chambertapering towards the rear, a Venturi tube connecting said collectingchamber and said distributing chamber, an exterior shell surroundingsaid distributing chamber, said shell having a form adapted to createzones on its exterior surface with reduced air pressure,'outlet openingsin the wall of said dis tributing chamber and means for conductingthe-gas currents first towards the front end of said shell and thenalong the inside thereof to outlet openings located in said zones ofreduced air pressure.

6. An exhaust silencer for aircraft motors and the like, comprising acollecting chamber adapted to be connected to the exhaust conduit fromthe motor, a distributing chamber, said collecting chamber anddistributing chamber being both conicallv shaped and having their basesturned towards each other, a Venturi tube connecting said collectingchamber and said distributing chamber, an exterior shell surroundingsaid distributin chamber, said shell having a form adapted to createzones on its exterior surface with reduced air pressure, outlet openingsin the wall of said distributing chamber and means for conducting thegas currents first towards I the front end of said shell and then alongthe inside thereof to outlet openings located in said zones of reducedair pressure.

7. An exhaust silencer for aircraft motors and the like, comprising acollecting chamber adapted to be connected to the exhaust conduit fromthe motor, a distributing chamber, a Venturi tube connecting saidcollecting chamber and said distributing chamber, an exterior shellsurrounding said distributing chamber, said shell having a form ada tedto create zones on its exterior surface witi reduced air pressure,outlet openings distributed along the wall of said distributing chamber,a baffle between said distributing chamber and the shell, said bafflehaving an inwardly projecting beaded rim at its front end adjacent thefront end of said shell so as to conduct the gas currents first towardsthe front through an annular opening of reduced cross section and thenalong the inside surface of said shell to outlet openings locatedadjacent the rear end thereof.

8. In an exhaust silencer for aircraft motors and the like, incombination, a plurality of exhaust conduits from the motor, acollecting chamber of streamline form communicating therewith, anexterior shell having the rear portion thereof deviating in axialdirection from said streamline form to create a zone'of turbulent airunder reduced pressure over part of the rear surface of said shell, andoutlet openings for the exhaust gases located at the part of said rearportion within said turbulent zone.

In testimony whereofJI affix my signature.

, OLE SOLBERG BIE.

